<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>fromCamelCase</title>
</head>

<body>
    <div>打开浏览器控制台查看结果</div>
    <script>
        const fromCamelCase = (str, separator = '_') =>
            str
                .replace(/([a-z\d])([A-Z])/g, '$1' + separator + '$2')
                .replace(/([A-Z]+)([A-Z][a-z\d]+)/g, '$1' + separator + '$2')
                .toLowerCase();
        console.log(fromCamelCase('someDatabaseFieldName', ' '));
    </script>
</body>

</html>